[PATCH] adapt page_lock_anon_vma() to PREEMPT_RCU

page_lock_anon_vma() uses spin_lock() to block RCU.  This doesn't work with
PREEMPT_RCU, we have to do rcu_read_lock() explicitely.  Otherwise, it is
theoretically possible that slab returns anon_vma's memory to the system
before we do spin_unlock(&anon_vma->lock).

[ Hugh points out that this only matters for PREEMPT_RCU, which isn't merged
  yet, and may never be.  Regardless, this patch is conceptually the
  right thing to do, even if it doesn't matter at this point.  - Linus ]

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: Christoph Lameter <clameter@engr.sgi.com>
Acked-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/mm/rmap.c b/mm/rmap.c
index 669acb22b572190ff2dcc6544c968bbd7516859e..22ed3f71a67421831f12b0deffa915eacf5d1db7 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -183,7 +183,7 @@ void __init anon_vma_init(void)
  */
 static struct anon_vma *page_lock_anon_vma(struct page *page)
 {
-       struct anon_vma *anon_vma = NULL;
+       struct anon_vma *anon_vma;
        unsigned long anon_mapping;
 
        rcu_read_lock();
@@ -195,9 +195,16 @@ static struct anon_vma *page_lock_anon_vma(struct page *page)
 
        anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
        spin_lock(&anon_vma->lock);
+       return anon_vma;
 out:
        rcu_read_unlock();
-       return anon_vma;
+       return NULL;
+}
+
+static void page_unlock_anon_vma(struct anon_vma *anon_vma)
+{
+       spin_unlock(&anon_vma->lock);
+       rcu_read_unlock();
 }
 
 /*
@@ -333,7 +340,8 @@ static int page_referenced_anon(struct page *page)
                if (!mapcount)
                        break;
        }
-       spin_unlock(&anon_vma->lock);
+
+       page_unlock_anon_vma(anon_vma);
        return referenced;
 }
 
@@ -802,7 +810,8 @@ static int try_to_unmap_anon(struct page *page, int migration)
                if (ret == SWAP_FAIL || !page_mapped(page))
                        break;
        }
-       spin_unlock(&anon_vma->lock);
+
+       page_unlock_anon_vma(anon_vma);
        return ret;
 }